Young adulthood is the developmental period when cigarette smoking becomes more entrenched, with dramatic increases in intensity occurring after age 18 (Hammond, 2005). In order for us to continue to make gains in reducing rates of cigarette smoking, we need to address the problem of smoking among young adults. This project will use Ecological Momentary Assessments (EMA) to gather real-time, naturalistic self reports of young adults' daily experiences and smoking behavior to examine how the immediate situation (proximal context) in which smoking occurs, along with the individual's subjective reactions to those experiences, varies by smoking level and influences future smoking behavior. This proposed project builds on several of our compelling findings to date with our current program project. These findings include: a) Mood just prior to smoking differs significantly from random, background times, such that when adolescents smoke, they feel less positive and more negative than other times. b) Following smoking, adolescents experience a significant relief of negative affect and boost in positive affect, c) Importantly, this change in affect predicts smoking trajectory - adolescents who belong to the trajectory with the lowest level of use and who do not escalate in their smoking derived the least amount of positive affective change following smoking; that is, these youth did not experience the boost following smoking, d) Mood variability, and not just overall level of mood, may be important in predicting escalation. e) Adolescents experience subjective aspects of withdrawal and dependence, even at relatively low levels of smoking. And f) Conjoint alcohol use and smoking may diminish the subjective mood boosts from smoking, although social context may be an important moderator. As we follow participants into young adulthood and as their smoking progresses, we will focus specifically on affective prompts and consequences to smoking, tracking of withdrawal symptoms, including new measures of attention, craving, as well as satisfaction with smoking, and the influence of alcohol and social contexts on smoking. This proposed project presents a unique opportunity to track and examine the development of dependence from adolescence through young adulthood. Thus, this project is well positioned to make a unique contribution to our understanding of the development of smoking patterns and nicotine dependence.